The getch, wgetch, mvgetch and mvwgetch, routines read a
character from the window. In no-delay mode, if no input
is waiting, the value ERR is returned. In delay mode, the
program waits until the system passes text through to the
program. Depending on the setting of cbreak, this is af-
ter one character (cbreak mode), or after the first new-
line (nocbreak mode). In half-delay mode, the program
waits until a character is typed or the specified timeout
has been reached.
If echo is enabled, and the window is not a pad, then the
character will also be echoed into the designated window
according to the following rules:
o If the character is the current erase character, left
arrow, or backspace, the cursor is moved one space to
the left and that screen position is erased as if
delch had been called.
o If the character value is any other KEY_ define, the
user is alerted with a beep call.
o If the character is a carriage-return, and if nl is
enabled, it is translated to a line-feed after echo-
ing.
o Otherwise the character is simply output to the
screen.
If the window is not a pad, and it has been moved or modi-
fied since the last call to wrefresh, wrefresh will be
called before another character is read.

If keypad is TRUE, and a function key is pressed, the to-
ken for that function key is returned instead of the raw
characters. Possible function keys are defined in <curs-es.h> as macros with values outside the range of 8-bit
characters whose names begin with KEY_. Thus, a variable
intended to hold the return value of a function key must
be of short size or larger.
When a character that could be the beginning of a function
key is received (which, on modern terminals, means an es-
cape character), curses sets a timer. If the remainder of
the sequence does not come in within the designated time,
the character is passed through; otherwise, the function
key value is returned. For this reason, many terminals
experience a delay between the time a user presses the es-
cape key and the escape is returned to the program.

The has_key routine takes a key-code value from the above
list, and returns TRUE or FALSE according to whether the
current terminal type recognizes a key with that value.
The library also supports these extensions:
define_key
defines a key-code for a given string (see de-fine_key(3x)).
key_defined
checks if there is a key-code defined for a given
string (see key_defined(3x)).

All routines return the integer ERR upon failure and an
integer value other than ERR (OK in the case of ungetch())
upon successful completion.
ungetch
returns ERR if there is no more room in the FIFO.
wgetch
returns ERR if the window pointer is null, or if
its timeout expires without having any data.
Functions with a "mv" prefix first perform a cursor move-
ment using wmove, and return an error if the position is
outside the window, or if the window pointer is null.

Use of the escape key by a programmer for a single charac-
ter function is discouraged, as it will cause a delay of
up to one second while the keypad code looks for a follow-
ing function-key sequence.
Some keys may be the same as commonly used control keys,
e.g., KEY_ENTER versus control/M, KEY_BACKSPACE versus
control/H. Some curses implementations may differ accord-
ing to whether they treat these control keys specially
(and ignore the terminfo), or use the terminfo defini-
tions. Ncurses uses the terminfo definition. If it says
that KEY_ENTER is control/M, getch will return KEY_ENTER
when you press control/M.
Generally, KEY_ENTER denotes the character(s) sent by the
Enter key on the numeric keypad:
o the terminal description lists the most useful keys,
o the Enter key on the regular keyboard is already han-
dled by the standard ASCII characters for carriage-re-
turn and line-feed,
o depending on whether nl or nonl was called, pressing
"Enter" on the regular keyboard may return either a
carriage-return or line-feed, and finally
o "Enter or send" is the standard description for this
key.
When using getch, wgetch, mvgetch, or mvwgetch, nocbreak
mode (nocbreak) and echo mode (echo) should not be used at
the same time. Depending on the state of the tty driver
when each character is typed, the program may produce un-
desirable results.
Note that getch, mvgetch, and mvwgetch may be macros.
Historically, the set of keypad macros was largely defined
by the extremely function-key-rich keyboard of the AT&T
7300, aka 3B1, aka Safari 4. Modern personal computers
usually have only a small subset of these. IBM PC-style
consoles typically support little more than KEY_UP,
KEY_DOWN, KEY_LEFT, KEY_RIGHT, KEY_HOME, KEY_END,
KEY_NPAGE, KEY_PPAGE, and function keys 1 through 12. The
Ins key is usually mapped to KEY_IC.

The *get* functions are described in the XSI Curses stan-
dard, Issue 4. They read single-byte characters only.
The standard specifies that they return ERR on failure,
but specifies no error conditions.
The echo behavior of these functions on input of KEY_ or
backspace characters was not specified in the SVr4 docu-
mentation. This description is adopted from the XSI Curs-
es standard.
The behavior of getch and friends in the presence of han-
dled signals is unspecified in the SVr4 and XSI Curses
documentation. Under historical curses implementations,
it varied depending on whether the operating system's im-
plementation of handled signal receipt interrupts a
read(2) call in progress or not, and also (in some imple-
mentations) depending on whether an input timeout or non-
blocking mode has been set.
Programmers concerned about portability should be prepared
for either of two cases: (a) signal receipt does not in-
terrupt getch; (b) signal receipt interrupts getch and
causes it to return ERR with errno set to EINTR. Under
the ncurses implementation, handled signals never inter-
rupt getch.
The has_key function is unique to ncurses. We recommend
that any code using it be conditionalized on the NCURS-ES_VERSION feature macro.